Patent GB-826678-A (GB)
Title: A cutter grinder
IPC: B23Q35/123
Filed: 1956-05-24
Abstract: 826,678. Copying machines. CINCINNATI MILLING MACHINE CO. May 24, 1956 [May 31, 1955], No. 16078/56. Class 40 (1). [Also in Group XXIII] A cutter grinder, Fig. 1, for automatically grinding helical cutter teeth includes a bed 20, a worktable 23 slidably mounted thereon, a grinding wheel 27 rotatably mounted on the bed adjacent the table, means e.g. an electric motor to rotate the grinding wheel, a head stock 35 and a tail stock 38 mounted on opposite ends of the table for movement therewith, means 43 for mounting the cutter 41 and a corresponding pattern 42 coaxially between the head stock and tail stock, a tracing mechanism 52 mounted on the bed and comprising a tracing finger 105 for engagement with a tooth of the mounted pattern, a motor 45 adapted for connection to the cutter and pattern for effecting synchronous rotation thereof, control means connected between the motor 45 and the tracing mechanism to control the operation of the motor in response to a change in position of the tracing finger on the pattern, the motor 45 being automatically controlled by the tracing mechanism during movement of the table to effect the synchronous rotation of the cutter and pattern to automatically maintain engagement between the pattern and tracing finger, such that the tracing finger tends to remain in a null position. The table 23 is mounted on a saddle 22 so that the cutter may be moved towards or away from the periphery of the grinding wheel. The tracing mechanism, Fig. 3, comprises a non-magnetic block 56 which is suspended in a box-like mounting member 69 by upper and lower strip spring members 70 and 72; the member 69 in turn is connected to a plate like member 75 through two vertical strip spring members. The member 75 is connected to the bed of the machine so that its height can be adjusted. The finger 105 is mounted on an arm 106 which is attached to the block 56 by means of a bolt 108 which passes through an oversized hole in the arm so that the finger can move to the right as shown in Fig. 3 against the pressure of a spring 112 when the pattern is rotated to bring the finger into engagement with another tooth. Rotation of the finger relative to the block 56 is prevented by means of an extension 110 which engages a slot 111 in the block. A bore in the block 56 contains a former 61 on which is wound the primary winding 58 and secondary windings 59 and 60 of a linear differential transformer. A powdered iron core 63 is mounted within the former 61, an extension 90 at one end engaging a V-groove in an adjustable block 84 which fixes the position of the core relative to the member 75. Thus, as the block 56 is moved by the engagement of the finger 105 with a tooth of the pattern the transformer windings move relative to the core 63. The transformer primary is excited by a 400-cycle alternating current from a RC oscillator and its secondary windings are connected in opposition so that when the core is symmetrically disposed in relation to the secondaries, there is no resultant output, i.e. the finger is then in the null position. The secondary windings of the transformer are connected to a conventional phase-sensitive rectifier, Fig. 8, which produces a D.C. output voltage, the polarity of which depends upon whether the output voltage of the linear transformer is in-phase or out-of-phase with the oscillator voltage. The output voltage at terminals 193, 194 of the rectifier are amplified by a bridge-connected power amplifier and applied to a transducer 208, Fig. 7, which forms part of the control means for the motor 45 which is an hydraulic motor. The transducer 208 is similar to a loud-speaker-type motor and comprises a coil 199 (not shown) which is fed from the amplifier and which is mounted in an annular gap in a magnetic circuit so that the position of the coil 199 depends upon the amplitude and polarity of the current flowing in it. The coil 199 is connected to the plunger 216 of an hydraulic servo-valve 209 which controls the supply of pressure fluid from a source 238 to the motor 45 so that it can rotate in either direction or be stationary depending upon the position of the plunger 216. The plunger 216 is connected to the movable core 221 of a linear differential transformer 185, Fig. 8, the primary of which is fed from the 400-cycle oscillator through a potentiometer 223 and the secondaries of which are connected in opposition and also in series with the secondaries of the transformer in the tracing mechanism; the arrangement is such that the resultant voltage in the secondaries of the transformer 185 oppose those in the secondaries of the transformer in the tracing mechanism and when the finger of the tracing mechanism is moved from its null position the error voltage produced in the secondary windings 59 and 60 moves the plunger 216 of the servo-valve 209 in a direction such that the motor 45 is rotated to return the tracing finger to its null position, the movement of the plunger 216 causing a voltage to appear in the secondary of the transformer 185 which balances the error voltage in the tracing mechanism transformer secondaries so that the current in the coil 199 of the transducer 208 is reduced to zero ; as the tracing finger 105 returns to its null position the error voltage from the transformer secondaries 59 and 60 is reduced and the bucking voltage from the transformer 185 is then the greater; this produces a signal in the coil 199 so as to move the plunger 216 of the servo-valve in the opposite direction and so cut off the motor 45. The potentiometer 223 controls the sensitivity since when the slider is at its right hand end as shown in Fig. 8 the amplitude of the voltage supplied to the primary winding is increased and the movement of the core 221 and hence of the plunger 216 necessary to produce a bucking voltage of given amplitude is reduced; the decreased movement of the plunger 216 thus causes less rapid operation of the tracing mechanism to move the finger back to its null position. The table 23 is moved by a feed motor so that the tracing finger traverses the length of the pattern and the grinding wheel traverses the length of the cutter and when the tracing finger runs off the end of the pattern and moves a predetermined extent from the null position a thyratron circuit is energized from the power amplifier so that a solenoid SOL3, Fig. 7, is energized and a solenoid SOL2 is de-energized to move an hydraulic indexing valve 230 from the position shown in Fig. 7 towards the left. This movement of the valve 230 disconnects the servo-valve 209 and instead connects a cylinder 242 to the hydraulic pressure source 238 and a piston 250 on the cylinder then delivers a measured amount of hydraulic fluid to the motor 45 so that both the pattern and cutter are rotated to bring the next cutter tooth into the grinding position and the next pattern tooth into position for engagement by the tracing finger. The engagement of the tooth by the tracing finger re-connects the pressure source to the valve 209. An adjustable stop 351 is provided in the cylinder 242 to determine the amount of fluid supplied to the motor 45 from the cylinder 242 which depends upon the pitch of the teeth of the cutter 41. The extent of movement of the table 23 is controlled by limit switches 1LS and 2LS which through relays control the direction of rotation of the table feed motor and a pressure switch IPS is also provided in the hydraulic system so that the reverse movement of the table 23 cannot commence until the cutter and pattern are rotated to their new positions. When all the cutter teeth have been ground a dog mounted on the pattern stops the operation of the machine.